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Tool/software:
The BQ24780EVM schematic in the reference design shows a voltage divider, setting the voltage at the ILIM pin (nominally) at 0.793V:
The data sheet for the BQ24780S provides the following equation to calculate the maximum charge current:
7.6.9 Setting the Charge Current
To set the charge current, write a 16-bit ChargeCurrent() command (0x14H or 0b00010100) using the data
format listed in Table 12. With 10-mΩ sense resistor, the bq24780S device provides a charge current range of
128 mA to 8.128 A, with 64-mA step resolution. Upon POR, charge current is 0 A. Any conditions for ACOK low
except ACOV resets the ChargeCurrent() to 0. Sending ChargeCurrent() 0 mA terminates charge.
To provide secondary protection, the bq24780S has an ILIM pin with which the user can program the maximum
allowed charge current. Internal charge current limit is the lower one between the voltage set by
ChargeCurrent(), and the voltage on ILIM pin. To disable this function, the user can pull ILIM above 2 V, which is
the maximum charge current regulation limit. When ILIM is below 60 mV, battery charging is disabled. The
preferred charge current limit can be derived from below equation:
Since the EVM uses a 10mΩ current sense resistor as recommended in the data sheet, this would seem to limit the maximum charge current to
(0.793)/(20 * .01) = 3.97A.
And yet all the TIDA-00657 documentation describes (and has charts for) output currents up to 8A.
Is the equation incorrect, or is the output current of the EVM limited to ~4A?
Hi Jeff,
Thanks for your post. We are currently in US holiday. A team member will get back to you on this later this week.
Hi Jeff,
The equation is still valid. The test report showed extended charge current range by temporarily disabling the external current limit.
Regards,
Tiger